Chip seal, as a surface treatment for pavement maintenance, has long been used. In such a method a layer of a rapid setting aqueous asphaltic emulsion is distributed onto the pavement to be repaired, and then an aggregate is applied thereto. Upon contact, the aggregate causes the rapid setting emulsion to set rather quickly and one of the advantages of this technique is that it allows highways, roads and other pavements being repaired to be reopened to traffic in a rather short order. The aggregate employed, which is commonly also referred to as stone, generally has a size on the order of about one-quarter inch to about one-half inch, and may be calcareous, siliceous or granitic in nature. It will readily be appreciated that in such chip seal techniques it is extremely important that the asphalt of the emulsion have strong adhesion to the stone to prevent its being dislodged and causing damage to windshields and the like. The previously employed asphaltic emulsions need improvement with respect to the adhesion of the aggregate and likewise need improvement with regard to other properties of the resulting wearcourse produced by the chip seal technique.
One approach that has been taken is to blend a rubber latex with the chip seal rapid setting aqueous asphaltic emulsion. While some improvement in properties has resulted from this technique, nonetheless there is still a problem in that the latex has a pronounced tendency with time to phase separate and adversely impact on the properties of chip seal layer.
In accordance with the present invention an improved chip seal method is provided by providing for an asphaltic emulsion which has improved adhesion to the chip seal stone, or aggregate, and which provides other desirable properties including homogeneity, less stripping, improved flexibility, particularly at low temperatures, improved strength and toughness, reduced high temperature flow and increased durability.
These improvements are obtained in accordance with the present invention by blending with a conventional rapid setting emulsion typically employed in the past for chip seal applications, prior to distribution onto the pavement, effective aggregate retention improving amounts of an aqueous emulsion of the prereacted reaction product of an acrylamide, asphalt having a viscosity of less than about 120,000 cps. (at 140.degree. F.), a vinyl aromatic monomer and a rubbery polymer.